The β-d-manno-heptoses are immune agonists across kingdoms

Area of Science:

• Immunology
• Microbiology
• Biochemistry

Background:

• Bacterial metabolites, such as ADP-heptose, are known innate immune agonists.
• The distribution and function of nucleotide-diphosphate-heptose biosynthetic enzymes (HBEs) across different life forms are not fully understood.

Purpose of the Study:

• To investigate the prevalence and function of HBEs and their synthesized heptose metabolites.
• To characterize novel heptose metabolites as potential immune agonists.
• To elucidate the cross-kingdom role of heptose metabolites in innate immunity.

Main Methods:

• Bioinformatic analysis to identify conserved motifs (STT_R5) in HBEs.
• Enzymatic assays to confirm the synthesis of ADP-, CDP-, and UDP-heptose.
• In vitro and in vivo assays using human and mouse cells and animal models to assess immune responses triggered by different heptose metabolites.
• Heterologous production of ADP-heptose in archaea.

Main Results:

• Functional HBEs and the conserved STT_R5 motif are widespread across bacteria, archaea, eukaryotes, and viruses.
• CDP- and UDP-heptoses were identified as novel heptose metabolites synthesized by these enzymes.
• CDP- and UDP-heptoses elicited significantly stronger alpha-protein kinase 1 (ALPK1)-dependent immune responses compared to ADP-heptose in mammalian systems.
• ADP-heptose produced in archaea retained its innate immune agonist activity.

Conclusions:

• β-d-manno-heptoses, including ADP-, CDP-, and UDP-heptose, are conserved, cross-kingdom pathogen-associated molecular patterns.
• These metabolites activate the ALPK1-dependent innate immune signaling cascade, highlighting a conserved immune recognition pathway.
• The findings expand our understanding of innate immunity and microbial-host interactions.